Yearly variation in individual diet specialization: Evidence from cave salamanders

Individual diet specialization is a key behavioral trait, with multifaceted impacts on population dynamics. Long-term studies are fundamental to properly understand such dynamics and their main causes. Indeed, individuals may vary from specialism to generalism in response to multiple biological and environmental factors, thus snapshot studies can have limited relevance for the overall biology of species. Yet, so far longitudinal studies testing the potential variation of diet specialization through time are lacking. Here we present the results of a study on individual diet specialization performed over a four-year period. Using three populations of the Ambrosis' cave salamander Speleomantes ambrosii we tested: i) whether seasonal variation in the occurrence of specialized individuals is maintained through different years, and ii) if the degree of specialization observed in a single season is constant through different years. Our results showed that the species maintains a high proportion of specialized individuals in spring and more generalist in autumn during different years, confirming a consistent seasonal variation of trophic specialization through time. On the other hand, the proportion of specialized individuals of the same period can vary up to ten-fold across years, suggesting that a single study may be not enough to properly understand the dynamics of a species' trophic niche. This study highlights the need of repeated surveys to accurately understand this behavioral trait, especially for species that are strongly dependent on local environmental conditions.